A wheel rim is an annular metallic sleeve that is radially stepped in several locations so as to be generally outwardly U-shaped. A tire is engaged radially outside such a rim, with its beads against the confronting inside faces of the end flanges of the rim, and a center is attached inside the rim so it and the tire can be mounted on a wheel hub. Normally the center is a plate having a central hole that fits over the wheel hub and that is formed with an array of radially equispaced smaller holes surrounding the central hole and serving to bolt the center to the wheel hub. The outer edge of the plate is usually formed with bent-over tabs that are welded centrally to the inner periphery of the rim.
The rim is formed from a piece of rectangular steel strip that is first bent into a cylindrical shape and welded permanently together so as to form a so-called ring blank. The desired profile is imparted to this blank by rolling it between complementarily shaped rollers that appropriately deform the blank as they rotate and orbit it through them. Since the necessary profiling is relatively deep it is necessary to do it normally in two separate stages in the first of which an intermediate profile is formed and in the second of which the final profile is imparted to the workpiece.
The roll-shaping machines each have a inner roll which is outwardly grooved and of the same profile as that which is to be imparted to the workpiece in the respective station and an outer roll that has a positive version of this profile. The blank or partly shaped workpiece is fitted axially over the inner roll and the rolls are moved radially together and simultaneously rotated so as to roll the desired profiled into the workpiece.
In order to spread out roll wear it is necessary to make them as big and thereby increase the time between changes. In addition since the rolls are mounted only at one end, so that the workpiece can be slipped over one of them, a larger diameter makes the roll stiffer and easier to support solidly. Thus the inner roll is normally made of a maximum diameter that is less than the minimum diameter that the workpiece will have after roll-shaping by a relatively small radial distance or play.
As a result it is necessary to fit the workpiece blank over and remove it from the inner roll by holding the workpiece so it is centered on the axis of the inner roll, and then moving the workpiece purely axially. If the accuracy of the axial motion is good it is possible to work with very small radial play. If there is any nonaxial vector to the transport direction the play has to be increased, with a corresponding loss in wear-resistance and so on, to allow for it.
Thus the standard such machines have complex holder arrangements that move in squared-off U-section paths each having one leg parallel to the axis of the respective shaper or a loading or unloading machine and a base extending transversely between these legs. The workpiece is thus gripped and moved first in a straight line from the loading station or a shaper, then the displacement direction is shifted 90.degree. and the workpiece is moved along into axial line with the next station, whereupon the displacement shifts through 90.degree. again to move it onto a shaper or into the unloading machine. Typically the workpiece is accelerated from a standstill at the start of each of the three parts of its U-shaped displacement and is decelerated at the end of each portion. Obviously, in a large-scale mass-production operation this consumes quite a bit of energy for transporting the workpieces alone, and subjects the conveyor to substantial wear and tear.